Mobile electronics devices are a ubiquitous part of modern life. Medical devices (e.g., pacemakers, hearing aids), telecommunications devices (e.g., pagers, cellular telephones), computing devices (e.g., laptop and tablet computers), navigation devices (e.g., satellite navigation receivers), entertainment devices (e.g., digital music players, still and video cameras), and innumerable portable electronic devices used in a wide variety of jobs (e.g., portable point-of-sale devices), to name but a few, all run on battery power. Many such devices include electronic circuits that require power to be supplied at different voltages. Additionally, the Direct Current (DC) voltage supplied by a battery varies over time, as the battery slowly loses power over its lifetime, or between recharges. A DC-DC converter is an electrical circuit typically employed to convert an unpredictable battery voltage to one or more continuous, regulated, predetermined DC voltage levels, which provide power to electronic circuits. Numerous types of DC-DC converters are known in the art. The term “buck” converter has been used to describe a DC-DC converter that outputs a lower voltage than the DC source (such as a battery); a “boost” converter is one that outputs a higher voltage than its DC input.
One important class of buck DC-DC converters, which operates with a relatively high efficiency and thus enhances battery life, is a form of switched mode power supply (SMPS). A SMPS buck DC-DC converter rapidly switches power from a DC source, such as a battery, to an energy storage element such as an inductor or capacitor, and then outputs the power at a predetermined voltage level. The output voltage level may be maintained by timing the switches transferring the power, based on a feedback control system
FIG. 1 depicts a simplified block diagram of a switching buck DC-DC converter 10. A power stage 12 comprises two series-connected transistors M0 and M1 implementing electronic switches, alternately connecting the node LX to a DC source power level (e.g., a battery voltage VBAT) and a lower voltage, such as ground. An inductor L stores energy from the source in a magnetic field. The amount of power output by the inductor to a load is controlled by the timing of the switches M0 and M1. An output capacitor C may be added to store charge and smooth the output voltage. A control circuit 30 regulates the switching of the transistors, in response to a feedback signal monitoring the output voltage or current
A SMPS may be operated in a different control modes, which may be dictated by operating conditions such as the power demanded by the load. Various DC-DC SMPS operating modes, each appropriate for different circumstances, are known in the art. However, switching between operating modes as conditions change remains a challenge in DC-DC converter controller design. Prior art multi-mode DC-DC converters experience undesirable transients, such as overshoot, undershoot, or increases in ripple current, when switching between operating modes.
The Background section of this document is provided to place embodiments of the present invention in technological and operational context, to assist those of skill in the art in understanding their scope and utility. Unless explicitly identified as such, no statement herein is admitted to be prior art merely by its inclusion in the Background section.